In a communication system based on the Wideband Code Division Multiple Access (WCDMA) technologies, there are dedicated channels and common channels. The common channels include a common pilot channel and a paging channel. The dedicated channels used by different users share the same time slot and the same frequency band with most of the common channels. In general, theses dedicated channels and common channels are transmitted synchronously and are distinguished from each other by disrelated “codes”, such as Orthogonal Variable length Spreading Frequency (OVSF) codes. At a receiver end, supposing that there is no multi-path and the synchronization is accurate when demodulating, the channels using the orthogonal codes do not interfere with each other.
However, some channels do not use codes orthogonal to those of other channels and do not occupy the whole time slot. For example, as shown in FIG. 1, a primary/secondary synchronization signal occupies the first 256 chips of each time slot. Thus, the primary/secondary synchronization signal is a sequence with period of a time slot and a duty ratio of 255/2560=1/10. Since not using the orthogonal code, the primary/secondary synchronization signal is an interference with period of a time slot to signals of other channels in the wireless channel.
FIG. 2 is a flowchart illustrating the framing of downlink data to be transmitted to a wireless channel. After multiplexing of different transport channels and before being sent to the wireless channel, data from different transport channels need a 2nd interleaving to disturb sequence therebetween. The 2nd interleaving will be hereinafter introduced briefly. Refer to 3 GPP TS25.212 V5.4.0 for details.
The process of the 2nd interleaving mainly includes: writing data into a matrix with size of N×30 row by row first; permuting columns of the matrix and reading the data from the matrix column by column. The rule of the inter-column permutation is listed as follows: supposing that the original order of the columns are 0, 1, 2, . . . , 29, the order of the columns after inter-column permutation is <0, 20, 10, 5, 15, 25, 3, 13, 23, 8, 18, 28, 1, 11, 21, 6, 16, 26, 4, 14, 24, 19, 9, 29, 12, 2, 7, 22, 27, 17>.
The 2nd interleaving is hereinafter described with reference to the schematic diagrams of data transmission shown in FIG. 2 and FIG. 3, and take the multiplexing of three transport channels A, B, and C in the WCDMA system to a physical channel as an example. Supposing that the data of the three transport channels are A1˜A30, B31˜B90 and C91˜C180, respectively, the process of the 2nd interleaving includes:
a channel multiplexing unit multiplexes the transport channels, A, B and C to get data <A1, A2˜A30, B31, B32˜B90, C91, C92˜C180>, which is to be interleaved with the 2nd interleaving.
Then, write the data into an interleaving matrix of an interleaving memory row by row and get a matrix as follows:
                                                          0                                                                                                    ⁢          1                                                                                                                                                                          2                                                                                        …                                                          28                                                          29                                                    ⁢          [                              A          ⁢                                          ⁢          1                                      A          ⁢                                          ⁢          2                                      A          ⁢                                          ⁢          3                            …                              A          ⁢                                          ⁢          29                                      A          ⁢                                          ⁢          30                                              B          ⁢                                          ⁢          31                                      B          ⁢                                          ⁢          32                                      B          ⁢                                          ⁢          33                            …                              B          ⁢                                          ⁢          59                                      B          ⁢                                          ⁢          60                                              B          ⁢                                          ⁢          61                                      B          ⁢                                          ⁢          62                                      B          ⁢                                          ⁢          63                            …                              B          ⁢                                          ⁢          89                                      B          ⁢                                          ⁢          90                                              C          ⁢                                          ⁢          91                                      C          ⁢                                          ⁢          92                                      C          ⁢                                          ⁢          93                            …                              C          ⁢                                          ⁢          119                                      C          ⁢                                          ⁢          120                                              C          ⁢                                          ⁢          121                                      C          ⁢                                          ⁢          122                                      C          ⁢                                          ⁢          123                            …                              C          ⁢                                          ⁢          149                                      C          ⁢                                          ⁢          150                                              C          ⁢                                          ⁢          151                                      C          ⁢                                          ⁢          152                                      C          ⁢                                          ⁢          153                            …                              C          ⁢                                          ⁢          179                                      C          ⁢                                          ⁢          180                      ]
Perform the inter-column permutation of the matrix and get an output as follows:
                                                          0                                                                                                    ⁢          20                                                                  10                                                          …                                                          27                                                          17                                                    ⁢          [                              A          ⁢                                          ⁢          1                                      A          ⁢                                          ⁢          21                                      A          ⁢                                          ⁢          31                            …                              A          ⁢                                          ⁢          28                                      A          ⁢                                          ⁢          18                                              B          ⁢                                          ⁢          31                                      B          ⁢                                          ⁢          51                                      B          ⁢                                          ⁢          41                            …                              B          ⁢                                          ⁢          58                                      B          ⁢                                          ⁢          48                                              B          ⁢                                          ⁢          61                                      B          ⁢                                          ⁢          81                                      B          ⁢                                          ⁢          71                            …                              B          ⁢                                          ⁢          88                                      B          ⁢                                          ⁢          78                                              C          ⁢                                          ⁢          91                                      C          ⁢                                          ⁢          111                                      C          ⁢                                          ⁢          101                            …                              C          ⁢                                          ⁢          118                                      C          ⁢                                          ⁢          108                                              C          ⁢                                          ⁢          121                                      C          ⁢                                          ⁢          141                                      C          ⁢                                          ⁢          131                            …                              C          ⁢                                          ⁢          148                                      C          ⁢                                          ⁢          138                                              C          ⁢                                          ⁢          151                                      C          ⁢                                          ⁢          171                                      C          ⁢                                          ⁢          161                            …                              C          ⁢                                          ⁢          178                                      C          ⁢                                          ⁢          168                      ]
Then, read the data from the interleaving matrix of the interleaving memory column by column and send the data to the wireless channel. The data read from the interleaving matrix is shown as follows.
  <                              A          ⁢                                          ⁢          1          ⁢                                          ⁢          B          ⁢                                          ⁢          31          ⁢          B          ⁢                                          ⁢          61          ⁢          C          ⁢                                          ⁢          91          ⁢                                          ⁢          C          ⁢                                          ⁢          121          ⁢          C          ⁢                                          ⁢          151                                      A          ⁢                                          ⁢          21          ⁢          B          ⁢                                          ⁢          51          ⁢          B          ⁢                                          ⁢          81          ⁢          C          ⁢                                          ⁢          111          ⁢          C          ⁢                                          ⁢          141          ⁢          C          ⁢                                          ⁢          171                            …                              A          ⁢                                          ⁢          18          ⁢          B          ⁢                                          ⁢          48          ⁢          B          ⁢                                          ⁢          78          ⁢          C          ⁢                                          ⁢          108          ⁢          C          ⁢                                          ⁢          138          ⁢          C          ⁢                                          ⁢          168                      >
Through analyzing the above interleaving process, it can be seen from the interleaving matrix: after the data of the three transport channels are sequentially written into the interweaving matrix, the data of the transport channel A are written into the beginning several rows of the interleaving matrix, the data of the transport channel B are written into the next several rows, and the data of the transport channel C are written into the further next several rows. The above inter-column permutation cannot change such a layout of the data. Furthermore, when the data of the interweaving matrix are read column by column, each data frame read includes 30 groups of array of “data of the transport channel A+data of the transport channel B+data of the transport channel C” because of the layout.
In the WCDMA system, each data frame is composed of 15 time slots while the data read from the interweaving matrix have 30 groups. Thus, each group corresponds to a half time slot in a frame. A diagram illustrating the relationship between data distribution and data period is shown in FIG. 4 which is obtained according to the distribution of the positions of the transport channels A, B and C in each group.
On the other hand, as described above, the primary/secondary synchronization signal in the WCDMA system forms a burst interference with period of a time slot. As shown in FIG. 5, which is a diagram illustrating the relationship of the data and the primary/secondary synchronization signal, the interference becomes an interference sequence to the wireless channel. Thus, when a mobile station receives, through the wireless channel, a signal interfered by the primary/secondary synchronization signal, after each transport channel is demultiplexed, it is probable that all the interference brought by the primary/secondary synchronization signal occurs in one transport channel. As a result, the performance of the transport channel affected by the interference is deteriorated. Thus, subsequent de-coding is deteriorated and even the communication quality is influenced, such as link break up.